Picophytoplankton predominance in hypersaline lakes (Transylvanian Basin, Romania)

Abstract

The occurrence and importance of photoautotrophic picoplankton (PPP, cells with a diameter <2 μm) was studied along a trophic and salinity gradient in hypersaline lakes of the Transylvanian Basin (Romania). The studied lakes were found to be rich in PPP, with abundances (maximum: 7.6 x 10 6 cells mL -1 ) higher than in freshwater and marine environments of similar trophic conditions. The contribution of PPP to the total phytoplankton biovolume did not decrease with increasing trophic state as it was generally found in other aquatic environments. Regardless of the trophic conditions, the contribution of PPP could reach 90-100% in these hypersaline lakes.We hypothesized that the PPP predominance might be the result of the low grazing pressure, since heterotrophic nanoflagellates (the main grazers of PPP) were absent in the studied samples.There were significant differences in community composition among the lakes along the salinity gradient. CyPPP predominated in less saline waters (mainly below 5%), while EuPPP were present along the entire salinity range (up to 18.7%), dominating the phytoplankton between 3 and 13% salinity. Above 13% salinity, the phytoplankton was composed mainly of Dunaliella species.

Winter Planktonic Microbial Communities in Highland Aquatic Habitats

“…1B, Table 2). Former studies (Schapira et al 2010;Somogyi et al 2014) reported that eukaryotic algae are the dominant in the picophytoplankton of saline environments between salinities 5 and 13%, which corresponded well with our observations.…”

“…However, it has been proven that natural aquatic habitats may harbour abundant planktonic communities in the coldest period of the year (Philips and Fawley 2002; Somogyi et al 2014), surprisingly even blooms of planktonic phototrophs could emerge (Álvarez et al 2009;Pálffy et al 2014;Somogyi et al 2009;Üveges et al 2012). Since microorganisms of inland waters have a great impact on biogeochemical cycles, may effect water quality and interact with other aquatic organisms, describing the taxonomy and ecology of microbes present in winter is crucial to understand their role in the ecosystem (Bertilsson et al 2013).…”

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

“…In comparison with Ursu Lake, the photic zone of Fara Fund Lake hosts smaller communities of phototrophic microorganisms as shown by the low chlorophyll a content reported in this study (see Table 1) and by previous works (Keresztes et al, 2012). Thanks to our microscopy and molecular analyses (doi: 10.5061/dryad.2gm06), we consider that oxygen levels in the euphotic zone of Fara Fund Lake were mostly generated by the photosynthetic activity of Dunaliella algae (see also Somogyi et al, 2014). Microbial communities capable of organic carbon degradation were found to be distributed along the water column of the lake, spreading from the oxic (Halobacteriales and Nanohaloarchaeota) to the suboxic layers (Halanaerobacter, Halanaerobium and Halorhabdus) (Supplementary Table S6).…”

The role and composition of winter picoeukaryotic assemblages in shallow Central European great lakes

“…Other studies have come to similar conclusion, winter phytoplankton primary production has 613 been found to primarily depend on light rather than on nutrient availability in various water 614 bodies, such as an alkaline pan (Pálffy et al, 2014) and a humic, boreal lake (Tulonen et al, 615 1994). Grazing might also be a determining factor, but in winter zooplankton activity is 616 greatly limited.…”